R – How Use Item in Header Of Repeater in ASP.net with C#2008

I think you are attacking it from the wrong angle by trying to encode all posted data.

Note that a "<" could also come from other outside sources, like a database field, a configuration, a file, a feed and so on.

Furthermore, "<" is not inherently dangerous. It's only dangerous in a specific context: when writing strings that haven't been encoded to HTML output (because of XSS).

In other contexts different sub-strings are dangerous, for example, if you write an user-provided URL into a link, the sub-string "javascript:" may be dangerous. The single quote character on the other hand is dangerous when interpolating strings in SQL queries, but perfectly safe if it is a part of a name submitted from a form or read from a database field.

The bottom line is: you can't filter random input for dangerous characters, because any character may be dangerous under the right circumstances. You should encode at the point where some specific characters may become dangerous because they cross into a different sub-language where they have special meaning. When you write a string to HTML, you should encode characters that have special meaning in HTML, using Server.HtmlEncode. If you pass a string to a dynamic SQL statement, you should encode different characters (or better, let the framework do it for you by using prepared statements or the like)..

When you are sure you HTML-encode everywhere you pass strings to HTML, then set ValidateRequest="false" in the <%@ Page ... %> directive in your .aspx file(s).

In .NET 4 you may need to do a little more. Sometimes it's necessary to also add <httpRuntime requestValidationMode="2.0" /> to web.config (reference).

Use the server control instead of making an input control runat=server

 <asp:CheckBox id="whatever" runat="Server" />

When you set the value in your ItemDataBound, you use FindControl

CheckBox checkBox = (CheckBox)e.Item.FindControl("whatever");
checkBox.Checked = true;

When you get the items, you also use FindControl from the item in a foreach construct. Also, depending on how you databound it, the DataItem may no longer be there after a postback.

foreach (RepeaterItem item in myRepeater.Items)
{
    if (item.ItemType == ListItemType.Item 
        || item.ItemType == ListItemType.AlternatingItem) 
    { 
        CheckBox checkBox = (CheckBox)item.FindControl("whatever");
        if (checkBox.Checked)
        { /* do something */ }
    }
}

• Many people are tempted to 'safe cast' using the as operator with FindControl(). I don't like that because when you change the control name on the form, you can silently ignore a development error and make it harder to track down. I try to only use the as operator if the control isn't guaranteed to be there.

Update for: Which CheckBox is which? In the rendered html you'll end up having all these checkbox name like

ctl00_cph0_ParentContainer_MyRepeater_ctl01_MyCheckbox
ctl00_cph0_ParentContainer_MyRepeater_ctl02_MyCheckbox
ctl00_cph0_ParentContainer_MyRepeater_ctl03_MyCheckbox

You don't care what the names are because the foreach item.FindControl() gets them for you, and you shouldn't assume anything about them. However, when you iterate via foreach, you usually need a way to reference that back to something. Most of the time this is done by also having an asp:HiddenField control alongside each CheckBox to hold an identifier to match it back up to the correct entity.

Security note: there is a security issue with using hidden fields because a hidden field can be altered in javascript; always be conscious that this value could have been modified by the user before the form was submitted.